TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Plan for Technology Development
7.5.4 Vibration Isolation Testbed
Scope
During pre-Phase A stage, significant effort will be invested in developing high-fidelity models
of the candidate isolation designs. The analytical models will be correlated with existing test
data to ensure that the actual behaviors of the isolators are properly captured. These isolation
models will also be incorporated in the integrated model, combining structure, optics, and control
models, to support end-to-end disturbance-to-performance analyses. The objective during pre-
Phase A is to demonstrate the vibration suppression capabilities of the isolators via analysis and
show that the stability requirements described in the error budget can be met.
Since the vibration isolation architecture has significant implications to different subsystems
within the TPF-C system, system engineering trades that account for these interdependencies
must be completed before down-selecting the isolation architecture. The system-level trades will
take into account cost, risk, and how performance margins may affect other subsystems
requirements. By the end of pre-Phase A, the relative merits of different isolation point designs
will be assessed, and an isolation design will be selected based on its vibration-suppression
performance and the results of the system engineering trades. At this point, it is also necessary
to develop detailed test plans to improve the maturity level of the isolation component
technology and determine testbed requirements.
The Phase A isolation sub-system test is envisioned to use the flight payload isolator design
attached to mass simulators that mimic the mass and inertia of the payload and the spacecraft
(i.e., a 1:1 scaled test). The mass simulators will need to be gravity offloaded so that their
fundamental suspension frequencies are significantly below the isolator mode (on the order of
0.01-Hz suspension frequencies). The spacecraft mass simulator will be excited using 6 force
shakers arranged to give 6 DOF forcing (e.g., in a Stewart platform). Two types of tests will be
performed. The first type measures the 6 × 6 transfer function matrix from disturbance inputs to
payload response. The next type will measure the isolator performance when the motion at each
side of the isolator is actively driven to mimic the behavior of analytical models of the spacecraft
and the payload. The spacecraft mass simulator response will be actively driven to mimic the
behavior of the analytical flexible spacecraft model, driven by the reaction wheel disturbances.
The response at the payload interface will be actively driven to mimic the analytical model of the
payload. The performance metrics will be the optical stability of the payload analytical model.
The metrics for isolation acceptance will include the isolator resonant frequencies (below a
specified frequency), damping (greater than a given percent damping), and attenuation above the
isolator resonance (greater than a specified, frequency-dependent requirement). The test will
need to be conducted in a thermal-vacuum chamber since the damper performance is a function
of temperature, and joint pumping and acoustics can introduce additional damping. The input
forcing levels should be consistent with expected disturbance force magnitudes to ensure that
nonlinear effects show up properly in the test results. Test data must be comprehensive enough to
tune the isolator models, and to characterize variability and uncertainty in the isolator behavior.
The correlated isolator models (with uncertainty model) will be used to generate an improved
system performance prediction, with uncertainty bounds produced by isolator variability.
During Phase B, the isolation sub-system testbed will be integrated with the pointing testbed to
demonstrate the pointing and stability performance of TPF-C. This testbed should be a subscale
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